An increase in murine skeletal muscle peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC-1alpha) mRNA in response to exercise is mediated by beta-adrenergic receptor activation.
Level 5 - mechanism / opinion, no new human data
Animal in vivo and ex vivo laboratory experiment
PubMed 17446185 · doi:10.1210/en.2006-1646
What was done
Researchers evaluated whether adrenergic receptor activation mediates the exercise-induced increase in skeletal muscle PGC-1alpha mRNA. They tested pharmacological adrenergic receptor agonists (alpha, beta1, beta2, and beta3) and antagonists (propranolol, ICI 118,551) in C57BL/6J mice, in ex vivo rat epitrochlearis muscle, and in beta1/beta2/beta3-adrenergic receptor knockout (beta-less) mice. They also evaluated PGC-1alpha mRNA expression in gastrocnemius muscle following a 45-minute bout of treadmill running with and without adrenergic blockade or knockout.
What was found
In C57BL/6J mice, injection of the beta2-agonist clenbuterol increased skeletal muscle PGC-1alpha mRNA expression more than 30-fold, an effect blocked by propranolol; alpha-, beta1-, and beta3-agonists did not increase expression. Direct exposure to beta2-agonist also increased PGC-1alpha mRNA in isolated rat epitrochlearis muscle, but had no effect in beta-less knockout mice. A 45-minute treadmill run increased gastrocnemius PGC-1alpha mRNA 3.5-fold in wild-type mice. This exercise-induced increase was inhibited by approximately 70% by propranolol or the beta2-specific inhibitor ICI 118,551, and was 36% lower in beta-less mice compared to wild-type mice.
Why it matters
The study identifies sympathetic nervous system stimulation acting via beta2-adrenergic receptors as a primary physiological pathway driving exercise-induced PGC-1alpha transcription in rodent skeletal muscle.
Limits
The abstract provides no sample sizes (n) or variance measures. The experiments were conducted exclusively in rodent models and isolated muscle tissue, and the study measured short-term mRNA transcript abundance rather than translated PGC-1alpha protein levels or downstream mitochondrial biogenesis.
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